The present device relates to a wristwatch with an oscillation alarm.
In recent years, there has been developed and practiced in many field an ultrasonic motor which has its rotor rotated by a traveling-wave generated by making use of the extensions and contractions of a piezoelectric element. This ultrasonic motor needs no reduction gear train or the like partly because it is simply constructed by stacking planar parts and partly because it has the characteristics of low speed rotation and a high torque. Thus, the ultrasonic motor is advantageous in that a high torque can be obtained by a thin, compact and simple structure, so that its application to the field of a wristwatch is expected.
In the wristwatch, the alarm function is highly practical. Since, however, the alarming function of the prior art to generate a warning sound is sometimes annoying, it is desired to realize a soundless alarm watch. It is, therefore, conceivable to provide an oscillation alarm which is enabled to inform the time by positioning a weight at the outer circumference of the rotor of the aforementioned ultrasonic motor to have its center of gravity offset from the center of rotation and by rotating the rotor to generate oscillations due to the shift of the center of gravity. Although a specific structure relating to such oscillation alarm is not disclosed yet, an example is presented in FIG. 21. A vibration member 1 has a piezoelectric element 2 adhered thereto and has its opposite side formed with a comb-like projections 1. A rotor 3 has a sliding member 3a adhered to its contacting portion with the vibration member 1 and is integrally formed with a semicircular ridge 3b at its outer circumferential portion to offset the center of gravity from the center of rotations. When the rotor 3 is rotated, the eccentric center of gravity is moved to oscillate the whole structure including a plate 8.
When an impact such as a fall is applied to a wristwatch having an oscillation alarm and the structure shown in FIG. 21, a very strong force is applied to the ridge 3b of the rotor 3. In case the wristwatch is dropped from a height of 1 [m], an acceleration at the level of 10,000 to 20,000 G is established, as is well known in the art. Even if the weight of the rotor 3 is as small as 1 [g], for example, the force due to the impact is 10 to 20 [kg]. In case this impact is received, it is wholly borne by the vibration member 1 through the contacting portion between the sliding member 3a and the comb-like projections 1a. Here, the comb-like projections 1a are generally composed of a repetition of undulations which are made of a highly rigid metal so as to enhance the rotating performance. The sliding member 3a is also made of a resin or the like so as to enhance the rotating performance. When, therefore, an excessive force is applied to that contacting portion, a pressure flaw following the shape of the comb-like projections 1a is formed on the sliding member 3a. If this pressure flaw is formed, it establishes a cause for resistance against the rotation of the rotor, thus raising a problem of significantly lowering the rotating performance or making the rotation impossible.
On the other hand, in the oscillation motor structure of an electronic wristwatch with a soundless alarm, a large gap is formed by the holding member and by the rotor, the weight and the vibration member to allow invasion of impurities such as dust, as shown in FIG. 21. Thus, the oscillation motor structure has a drawback that the oscillation motor is liable to stop or operate with an inferior reliability.